Graph LLVM DAG中的粘合和链依赖关系是什么？

我对LLVM和编译器有些陌生

我决定使用以下命令生成一个DAG

llc -view-sched-dags hello_world.ll

我得到了一个包含不同依赖类型的非常大的图。《LLVM核心库入门》一书解释道：

黑色箭头表示数据流相关性
红色箭头表示粘合依赖性
蓝色虚线箭头表示链相关性

我清楚地记得在学校的编译器课上讲过数据流依赖性。但我不记得谈论过另外两个。有人能解释其他依赖项的含义吗？感谢您的帮助

你好_world.cpp

#include <stdio.h>
#include <assert.h>

int sum(int a, int b) {
  return a + b;
}

int main(int argc, char** argv) {
  printf("Hello World! %d\n", sum(argc, 1));
  return 0;
}

hello\u world.main.jpg

hello_world.sum.jpg

---

链依赖关系可防止具有副作用（包括内存操作和显式寄存器操作）的节点彼此之间的调度顺序混乱

“粘合”可防止两个节点在调度过程中断开。事实上，它比这更微妙[1]，但大多数时候你不需要担心它。（如果您要实现自己的后端，需要两条指令彼此相邻，那么您确实希望使用伪指令，并在调度完成后扩展伪指令。）

[1] ：例如见

; ModuleID = 'hello_world.cpp'
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

@.str = private unnamed_addr constant [17 x i8] c"Hello World! %d\0A\00", align 1

; Function Attrs: nounwind uwtable
define i32 @_Z3sumii(i32 %a, i32 %b) #0 {
entry:
  %a.addr = alloca i32, align 4
  %b.addr = alloca i32, align 4
  store i32 %a, i32* %a.addr, align 4
  store i32 %b, i32* %b.addr, align 4
  %0 = load i32* %a.addr, align 4
  %1 = load i32* %b.addr, align 4
  %add = add nsw i32 %0, %1
  ret i32 %add
}

; Function Attrs: uwtable
define i32 @main(i32 %argc, i8** %argv) #1 {
entry:
  %retval = alloca i32, align 4
  %argc.addr = alloca i32, align 4
  %argv.addr = alloca i8**, align 8
  store i32 0, i32* %retval
  store i32 %argc, i32* %argc.addr, align 4
  store i8** %argv, i8*** %argv.addr, align 8
  %0 = load i32* %argc.addr, align 4
  %call = call i32 @_Z3sumii(i32 %0, i32 1)
  %call1 = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([17 x i8]* @.str, i32 0, i32 0), i32 %call)
  ret i32 0
}

declare i32 @printf(i8*, ...) #2

attributes #0 = { nounwind uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #2 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }

!llvm.ident = !{!0}

!0 = metadata !{metadata !"clang version 3.5.0 "}